Application Of Transition Metal(Fe,Co)sulfur Compounds In Sodium Ion Batteries

In recent years,lithium-ion batteries?LIBs?have experienced rapid development for their high energy density,long cycle life,enhanced rate capability and environmental friendliness and have been widely applied in smart and portable electronic devices.However,due to the shortage in lithium reserves and uneven distribution of lithium resources,the price of lithium continues to rise,which seriously impedes further development for LIBs.In view of this,due to the abundant sodium resources,as well as similar electrochemical properties compared to LIBs and suitable redox potential,sodium-ion batteries?SIBs?have attracted more and more attentions.To date,the reported anode materials for SIBs still suffer from a series of problems,such as low specific capacity,poor rate capability and short cycle life,which significantly impedes the commercial application of SIBs.In this thesis,transition metal sulfides with different morphologies and structures are synthesized by facile strategies,and their electrochemical properties as anode materials for SIBs are intensively evaluated.The main experimental contents of this thesis are described as follows:?1?Preparation of carbon-coated iron sulfide by simple hydrothermal and high temperature vulcanization methods?Fe₇S₈@C?.Iron sulfides,as promising anode materials,have been intensively studied;however,they still suffers from limited cycle life caused by huge volume change during cycling.In the present work,a facile method has been demonstrated to prepare Fe₂O₃ nanobiscuits followed by poly?dopamine?coating.After thermally induced sulfurization,Fe₇S₈@C nanobiscuits have been successfully synthesized,which show high specific capacities,excellent rate capability and stable cycling stability as anodes for SIBs.The Fe₇S₈@C nanobiscuits exhibit high reversible capacity of 530.8 mA h g^-1 after 1000 cycles at high current density of 5 A g^-1.This outstanding electrochemical performance could be attributed to the stress-buffering effect owing to the biscuit-like nanostructure and conformal surface coating with carbon.?2?Preparation of tin,cobalt sulfide with hollow core-shell structure by coprecipitation and hydrothermal vulcanization?CoS₂/C@SnS₂?.An effective and controllable strategy has been presented to fabricate SnS₂-nanosheets coated CoS₂/C nano-hollow cubic composite?CoS₂/C@SnS₂?using Co-MOF as starting material.The CoS₂/C@SnS₂ electrode exhibits ultra-long cycle life and excellent rate performance as anodes for SIBs,which achieves high specific capacity retention of 400.1 mAh g^-1 at a current density of 10 A g^-11 even after 3500cycles.When used in full-cell,it also shows enhanced sodium storage capacity and delivers a high reversible capacity of 567.3 mAh g^-1 after 1000 cycles at 1 A g^-1.This strategy can pave a way for preparing various metal sulfides with fascinating structure and excellent performance for the potential application in energy storage area.